Observation of an intermediate state during lithium intercalation of twisted bilayer MoS2

Lithium intercalation of MoS2 is generally believed to introduce a phase transition from H phase (semiconducting) to T phase (metallic). However, during the intercalation process, a spatially sharp boundary is usually formed between the fully intercalated T phase MoS2 and non-intercalated H phase MoS2. The intermediate state, i.e., lightly intercalated H phase MoS2 without a phase transition, is difficult to investigate by optical-microscope-based spectroscopy due to the narrow size. Here, we report the stabilization of the intermediate state across the whole flake of twisted bilayer MoS2. The twisted bilayer system allows the lithium to intercalate from the top surface and enables fast Li-ion diffusion by the reduced interlayer interaction. The E-2g Raman mode of the intermediate state shows a peak splitting behavior. Our simulation results indicate that the intermediate state is stabilized by lithium-induced symmetry breaking of the H phase MoS2. Our results provide an insight into the non-uniform intercalation during battery charging and discharging, and also open a new opportunity to modulate the properties of twisted 2D systems with guest species doping in the Moire structures. Li intercalation of MoS2 induces a transition from the insulating H-phase to the metallic T-phase, with a sharp boundary in between. Here the authors stabilize the intermediate phase in twisted bilayer MoS2, by leveraging the Moire potential which facilitates fast Li diffusion and uniform intercalation.

Automated summary

The authors stabilize the intermediate phase in twisted bilayer MoS2, leveraging the Moire potential, which facilitates fast Li diffusion and uniform intercalation. This provides insight into non-uniform intercalation during battery charging and discharging, and opens up new opportunities for modulating the properties of 2D materials with guest species doping in Moire structures.